Description
- Abstract:
- Two-dimensional (2D) materials exhibit ultra-high strength due to their nearly perfect lattice structures but low fracture toughness due to their lack of effective energy dissipation mechanisms. To toughen 2D materials, here we investigate how cracks interact with topological defects, out-of-plane curvatures, three-dimensional (3D) geometry as well as interlayer interactions in atomically thin crystals and propose tough designs for 2D materials in different forms, including monolayers, nanotube hybrids, 3D nanolattices and multilayered systems, using multiscale modelling. We first study topological toughening in monolayer graphene and demonstrate that by designing the distribution of topological defects and out-of-plane curvatures, various toughening mechanisms, including crack tip blunting/trapping, fracture mode transition, bridging, crack deflection, void formation, daughter crack initiation and coalescence, can be activated in graphene and enhance the fracture toughness effectively. Next, we investigate the fracture process and toughening mechanisms in rebar graphene, a carbon nanotube-graphene hybrid. Our simulations unveil how the carbon nanotubes integrated onto graphene affect the crack and identify the key toughening mechanisms and their dependence on the geometry and distribution of carbon nanotubes, explaining the enhanced fracture toughness experimentally measured in rebar graphene. For 3D assemblies made of 2D materials, we study the structure instability in graphene surfaces and propose a reversible energy dissipation mechanism via snapping through. By mimicking the shell geometry of flexible straw, we construct bi-stable graphene units and build 3D nanolattices with them. Combining numerical simulations and theoretical analysis, we demonstrate this 3D graphene nanolattice can deform in a pseudoplastic way with a stress-strain hysteresis and becomes tolerant to crack-like flaws via effective energy dissipation. Finally, we focus on multilayered 2D materials and investigate the effect of interlayer interaction on crack propagation. By studying the crack propagation in the presence of neighboring layers, we demonstrate how interlayer interaction reduces the driving force at the crack tip and show its dependence on system size, in-plane modulus and interlayer shearing stress through theoretical analysis and numerical simulations. Combining fracture-controlled crack propagation and strength-controlled crack penetration, we provide a phase diagram for these two competing failure modes to predict the crack evolution in multilayered 2D materials.
- Notes:
- Thesis (Ph. D.)--Brown University, 2021
Citation
Ni, Bo,
"Topological Toughening and Fracture of 2D Materials"
(2021).
Mechanics of Solids Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://repository.library.brown.edu/studio/item/bdr:66a37msz/
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Mechanics of Solids Theses and Dissertations
Theses and Dissertations for the Mechanics of Solids department....